The fine structure of the limulus optic nerve

Two complete composite photographs of the optic nerve of Limulus, made by electron microscopy, reveal the presence of neurosecretory granules in the large axons of the rudimentary eye neurons. The number of intermediate sized, (3–7 μ), of eccentric cells corresponds with the number of ommatidia as expected, but only their sheath of Schwann cells show an intimate interfolding. Based on the number of fine axons within the nerve each ommatidium has an average of 12–13 retinular cells. The diameter of their fibers is between 0.2 and 3 μ although the majority are between 1 and 1.5 μ. They are aggregated into bundles of six to seven fibers by the sheath cells although some bundles contain only two, others as many as 181 fibers. There is no indication in these studies that retinular cell axons within a bundle are associated with the same, adjacent, or other pattern of ommatidia. The photographs suggest that physiological activity in retinular cell axons might be detected most easily in the smallest bundles because they contain the fewest, but the larger retinular cell axons.     

The differentiation of oligodendrocytes in the rat optic nerve

The time of appearance and the rate of accumulation of specific myelin lipids and proteins were measured in the rat optic nerve during the period from birth to 18 days. The appearance of the activities of several enzymes involved in the synthesis of these lipids was also monitored. Correlation of these biochemical data with previously known morphological findings indicated that the “active” oligodendrocytes (detected between 5 and 15 days after birth) displayed maximal levels of synthesis of the components of myelin, and that these cells appeared to be responsible for the initial synthesis of myelin. Both young and mature oligodendrocytes showed limited capacity to synthesize these compounds. Furthermore, induction of the enzymes involved in the synthesis of myelin components appeared to take place in a simultaneous, rather than a sequential manner.     

Mass of the optic nerve, the optic chiasm and the optic tract of practical medical importance

The intraorbital, intracanalicular, and intracranial length of the optic nerve was measured. Also the length of the optic tract between chiasm and lateral geniculate body was estimated. Included are the ampulla of the optic sheaths, the course of the ophthalmic artery, and the distance of the ciliary ganglion to the lateral margin of the orbit.     

Choroidal melanoma invading the optic nerve head

Choroidal melanoma is the most common primary intraocular tumor, however, involvement of the optic nerve is rare. This case report presents a patient with an amelanotic juxtapapillary malignant choroidal melanoma with secondary optic disc invasion. The clinical signs and symptoms, differential diagnosis, management and prognosis for survival are discussed.     

Electrical potentials from the eye and optic nerve of Strombus: effects of electrical stimulation of the optic nerve.

1. Photic stimulation of the mature eye of Strombus can evoke in the optic nerve 'on' activity in numerous small afferent fibres and repetitive 'off' bursts of afferent impulses in a smaller number of larger fibres. 2. Synchronous invasion of the eye by electrically evoked impulses in small optic nerve fibres (apparently the 'on' afferents, antidromically activated) can evoke a burst of impulses in the larger 'off' fibres which propagate away from the eye. Invasion of the eye via one branch of optic nerve can evoke an answering burst in another branch. 3. Such electrically evoked bursts are similar to light-evoked 'off' bursts with respect to their impulse composition, their ability to be inhibited by illumination of the eye, and their susceptibility to MgCl2 anaesthesia. 4. Invasion of the eye by a train of repetitive electrically evoked impulses in the absence of photic stimulation can give rise to repetitive 'off' bursts as well as concomitant oscillatory potentials in the eye which are similar to those normally evoked by cessation of a photic stimulus. 5. The electrically evoked 'off' bursts appear to be caused by an excitatory rebound following the cessation of inhibitory synaptic input from photoreceptors which can be antidromically activated by electrical stimulation of the optic nerve. 6. The experimental results suggest that the rhythmic discharge of the 'off' fibres evoked by the cessation of a photic stimulus is mediated by the abrupt decrease of inhibitory synaptic input from the receptors.     

Glaucoma and optic nerve repair

Glaucoma is a leading cause of irreversible blindness worldwide and causes progressive visual impairment attributable to the dysfunction and death of retinal ganglion cells (RGCs). Progression of visual field damage is slow and typically painless. Thus, glaucoma is often diagnosed after a substantial percentage of RGCs has been damaged. To date, clinical interventions are mainly restricted to the reduction of intraocular pressure (IOP), one of the major risk factors for this disease. However, the lowering of IOP is often insufficient to halt or reverse the progress of visual loss, underlining the need for the development of alternative treatment strategies. Several lines of evidence suggest that axonal damage of RGCs occurs primary at the optic nerve head, where axons appear to be most vulnerable. Axonal injury leads to the functional loss of RGCs and subsequently induces the death of the neurons. However, the detailed molecular mechanism(s) underlying IOP-induced optic nerve injury remain poorly understood. Moreover, whether glaucoma pathophysiology is primarily axonal, glial, or vascular remains unclear. Therefore, protective strategies to prevent further axonal and subsequent soma degeneration are of great importance to limit the progression of sight loss. In addition, strategies that stimulate injured RGCs to regenerate and reconnect axons with their central targets are necessary for functional restoration. The present review provides an overview of the context of glaucoma pathogenesis and surveys recent findings regarding potential strategies for axonal regeneration of RGCs and optic nerve repair, focusing on the role of cytokines and their downstream signaling pathways.     

少突胶质细胞和视神经损伤

少突胶质细胞在中枢神经系统中具有重要和广泛的生理功能。视神经损伤后,出现髓鞘脱失、少突胶质细胞死亡和髓鞘再生等病理改变,产生的髓鞘碎片能抑制视神经轴索再生。少突胶质细胞的抑制特性由特定的抑制分子介导,目前已鉴定的抑制分子主要有Nogo、髓鞘相关糖蛋白（myelin—associated glycoprotein,MAG）、少突胶质细胞髓鞘糖蛋白（oligodendrocyte myelin glycoprotein,OMgp）等,它们通过同一受体复合体传导抑制信号。阻滞抑制分子及其受体,或调整神经元的内在生长状态以克服抑制分子的抑制作用,可以促进视神经损伤后再生。本文就这方面的进展作一综述。     

Acquired pits of the optic nerve in glaucoma

An acquired pit of the optic nerve (APON) is a discrete, focal area of depression within the optic cup at the level of the lamina cribrosa. It is an under-diagnosed sign of glaucoma damage due to its subtle appearance. APONs occur more frequently unilaterally and in patients with normal-tension glaucoma (NTG). They often correspond to a deep, sharp-margined scotoma approaching or involving fixation. Given the location and progressive nature of the associated visual field defects, glaucoma patients and glaucoma suspects should be evaluated for this sign of localized optic nerve damage.     

The conduction of optic nerve fibers using different visual patterns

The Authors have studied the behaviour of checkerboard pattern visual evoked potential (VEP) latencies by using different spatial frequency stimuli and different stimulating visual fields in order to demonstrate whether spatial frequency might constitute a parameter capable of exciting different retinal regions like different stimulus fields. According to the recent literature low spatial frequency stimuli generate VEP with latencies which are significantly shorter than high spatial frequency stimuli, making this method more reliable for the differentiation of macular and peripheral retinal fields.     

The contribution of axoplasmic flow in optic nerve and protein synthesis within the optic tectum to synaptic membrane proteins of the chick optic tectum

In the 5-day-old chick, radioactive leucine was incorporated into proteins of synaptosomal and subsynaptosomal fractions both by fast axoplasmic flow and synthesis within the optic tectum. The distribution of radioactivity in subsynaptosomal fractions suggested that both pathways contribute to the protein constituents of each fraction. The relative contributions to each fraction were similar except for the supernatant proteins, for which fast axoplasmic flow contributed less than the synthesis within the optic tectum. The qualitative contribution of fast flow and synthesis within the optic tectum to the synaptic membrane fraction was distinctive. Fast axoplasmic flow preferentially labelled the high molecular weight proteins, whereas synthesis within the optic tectum labelled a larger percentage of smaller molecular weight proteins.